Peat-Wood Fly Ash as Cold-Region Supplementary Cementitious Material: Air Content and Freeze-Thaw Resistance of Air-Entrained Mortars

Fluidized bed combustion fly ash (FBCFA) is a promising industrial side stream to be used as a partial cement replacement material. Untreated and milled FBCFAs from cocombustion of peat and wood were used to replace 20% of portland cement in air-entrained and non-air-entrained mortars. Additionally, equivalent mortars containing fly ash from pulverized coal combustion (CFA) were prepared to compare FBCFAs with more conventional standardized cement replacement material. The study found that both FBCFAs produced mortars with similar compressive strengths compared to a reference, indicating that milling did not affect reactivity of ashes. Air-entrained FBCFA-containing mortars had about the same amount of entrained air compared to the reference mortar. FBCFAs outperformed CFA as a cement replacement material, which produced lower compressive strengths and reduced the amount of entrained air. Non-air-entrained mortar containing CFA suffered severe damage during the freeze-thaw (FT) experiment, unlike non-air-entrained mortars containing untreated or milled FBCFA. The addition of an air-entrainment agent improved FT resistance of all mortars, except those that contained milled FBCFA, which nevertheless had good FT resistance. This first-of-its-kind investigation of the suitability of peat-wood FBCFAs as a supplementary cementitious material in air-entrained mortars suggests a potential use of FBCFAs in cold-region concreting.